Why don't birds get shocked on power lines?

[Sooty]

Into the lions den! Lordie, what a contentious issue!
So, why are birds not shocked ? Errr.. they can be... with very high voltages...
Well, at the risk of starting a war here, I will offer you another slant on this matter that if I am correct, wasn't even mentioned by anyone else! And that is, that although the various models discussing capacitors and the pushing and pulling of electrons may be an aspect of the situation, considering our birds/helicopters as capacitors may be relatively minor to the question of 'being shocked'.
Yes?
Errr... yes. And what is the major factor?
Athmospheric Voltage Gradient... if the term doesn't upset somebody!
What's that all about? Well, when we are talking about massive voltages, it's not longer a case of 'in the conductor we have a voltage, and outside of the conductor, we don't'. With a few volts on our conductor, no big deal. However, when we have tens/hundreds of thousand of volts, we may have a voltage gradient created that may be of the order of 25kV per inch! That means that even if we come close to such a conductor without even touching it, we (and birds!) may not only be exposed to a high voltage gradient, but if the air is not especially dry (ie, damp, and so conductive!) such conducting air may be capable of providing enough -current- flow to be felt to a lesser or greater level!
"But what about -thousand of volts- of Static Electricity?" I can hear someone scream!
Well, that's the thing about 'static electricity'. It's 'harmless', not because it's 'a low voltage', but because it's being created in a scenario that is not capable of providing much -current-. After all, -power- (ie, that which can actually -do- something!) is the -multiple- of Voltage with Current - and voltage without current doesn't do much at all!
So, a power line is most definitely capable of providing a high current, (maybe that's why they cell 'em -Power- lines!) and when we/bird are in the middle of a high voltage gradient, a current may most definitely flow, and it's that current (not just voltage) that is a measure of what can be felt, and may harm us too!
As for -where- that flow may be -to-, the answer is, the environment/earth in the form of a Coronal Discharge.
Just to elaborate... (waffle some more?) it is interesting to see the pic in another post of a guy in a hoodie holding a sparking rod... but there is no explanatory caption...
So, I'll try to fill in a little. A hoodie...? Er, not really. A Faraday Suit! Eh? Like a Faraday Cage, except personal!
What is going on? Well, the guy is approaching a live high tension line, probably 'cos he has to work on it. Why hasn't it been shut down? Probably 'cos that would mean shutting down an entire area of the countryside. And anyway, with the right kit, he doesn't have to!
So, as he approaches the line, he reaches out with a conducting rod that is connected to his suit. This will bring -the suit's- voltage (and that of the guy inside!) up to that of the power line, (without any voltage gradients across any part of his body) and as we can see, (from the spark!) -massive- current is being passed! Not just because of the guy in the suit is acting as a capacitor, but because the power is passing into the suit, and then discharged into the environment -from the suit-, and -not- through/from the guy himself.
As for 'feeling it'... (ie, feeling the voltage gradient I mentioned above) I spoke to a friend who did this kind of work. And being an adventurous kind of guy, he said yes, he'd wondered about this too... and he decided to conduct a lill' experiment. Yes? He wondered what would happen if he tried -removing- his suit while connected up to a -very- high voltage line!
And what happened? Well, he said that as he began to open up his 'hoodie', (no rush!) he began to 'feel the electricity in the air'! And after he got the hood of the suit less than halfway off his head, he could stand it no more, and promptly put it back on!
Shocking stuff!

 

[Dale]

That voltage gradient is a result of the capacitance of the line, and the current is still the charging of a capacitor. You wrote as though you think what you described is a big controversial surprise, but it is what we have been discussing.

 

[thetrellan]

Yes, in my diagram the helicopter can be replaced by the bird just before touching the wire. The part of the bird closest to the power line, its feet, is one plate of capacitor C2, and the part that is furthest from the power line, say its head, is one plate of capacitor C2. When AC current is flowing through the bird's body, the excess charge is jumping between its head and feet. A little later, when the spark develops or when the bird is touching the wire, C2 is shorted out, and the excess charge is jumping between the bird's head and the "earth". The excess charge equals Q = CV = 150 kV · 10 pF = 1.5 μC = 10^13 electrons.

Yes, the size of the bird matters, smaller birds experience smaller currents, whereas larger birds and helicopters experience larger currents.

I know birds are small, but it's my understand that electricity takes the shortest route, which in the bird's case won't take it through the head, but from foot to foot. That much power would probably just fry the whole body, but still. When I nearly electrocuted myself I had my hand in a socket, and power flowed between just the last two fingers. I know this because you can still see entrance and exit wounds marked by the skin graft that followed. The rest of me didn't like that at all, of course. I was just a dumb preschooler, rooted to the spot, muscles frozen. A cousin tackled me to safety. My entire body was affected, but had I put both hands in travel would have been between them, likely stopping my heart along the way, but still not passing through the head.

 

[Michaela SJ]

Don't see birds on extra high voltage lines because of high density leakage and capacitive currents. EHV leakage currents would be unbearable for the birds.

I once watched a beautiful Golden Eagle land with a wing crossed over a transmission line and its other wing on the spreader. The eagle immediately combusted and caused enough damage that PG&E had to look at the tower from one of its helicopters.

It was always my understanding that birds do not exhibit enough of a path through their two legs for a current to leak off the less resisted transmission line.

I still carry the scar from leaning against a high voltage distribution line while climbing a tree when I was 10 years old. Simply being in the tree gave enough of a circuit through my arm to create a nasty burn.

 

[b.shahvir]

Electricity works in mysterious ways.

 

[davenn]

Electricity works in mysterious ways.

that's a poor misquote

in fact electricity is pretty well understood

 

[davenn]

. This will bring -the suit's- voltage (and that of the guy inside!) up to that of the power line

(NO)

if it were the case, there would be no point wearing the suit

 

[b.shahvir]

that's a poor misquote

in fact electricity is pretty well understood

There's a huge difference between 'pretty well' and 'perfectly'.

 

[davenn]

There's a huge difference between 'pretty well' and 'perfectly'.

it's well enough understood to totally negate your comment and has been for a long time

 

[Sooty]

(NO)

if it were the case, there would be no point wearing the suit

(YES)

The point of the suit is not to somehow 'stop the occupant's voltage from becoming that of the line'... it's to prevent voltage -gradients- from being created across any part of his body. What 'does the damage' is not the voltage per se... it's the current that flows solely 'cos a gradient permits it to do so. No gradient, no current... or is that (NO) also?

PS
If (NO), you forgot to explain what IS the point of wearing the suit...

 

[davenn]

PS
If (NO), you forgot to explain what IS the point of wearing the suit...

Unbelievable seriously !
It is as you stated but maybe you don't believe ... an example of a Faraday shield
The electric field DOES NOT penetrate the suit ... skin effect ensure that

There's a number of www sites that will give you that answer

you continue to contradict yourself ...

The point of the suit is not to somehow 'stop the occupant's voltage from becoming that of the line'... it's to prevent voltage -gradients- from being created across any part of his body.

 

[Sooty]

Unbelievable seriously !
It is as you stated but maybe you don't believe ... an example of a Faraday shield
The electric field DOES NOT penetrate the suit ... skin effect ensure that

There's a number of www sites that will give you that answer

you continue to contradict yourself ...

I never said it 'penetrated' anything. Believably! Seriously! Read it again - I said it prevents voltage -gradients- from being created across any part of his body.

PS - Any more examples of me 'continuing to contradict' myself?... maybe starting with one example of where I did actually contradict myself...

 

[davenn]

I never said it 'penetrated' anything. Believably! Seriously! Read it again - I said it prevents voltage -gradients- from being created across any part of his body.

So, as he approaches the line, he reaches out with a conducting rod that is connected to his suit. This will bring -the suit's- voltage (and that of the guy inside!)

Yes you did say it ... there is the contradiction !

to bring the guy's body inside up to the line voltage ... it MUST penetrate the suit DOH

and as I have told you, that doesn't happen ... the guy inside is shielded

 

[Sooty]

Hmmm...

The electric field DOES NOT penetrate the suit

followed by

to bring the guy's body inside up to the line voltage ... it MUST penetrate the suit DOH

Right, got it!

 

[Dale]

There's a huge difference between 'pretty well' and 'perfectly'.

It is, in fact, perfectly understood. There is no known EM phenomena which cannot be explained with our current EM theory. It can correctly give the outcome of every EM experiment performed to date.

 

[anorlunda]

The OP question has been answered over and over and over again.

Thread closed.

 

[Dale]

@davenn in this case @Sooty is correct.

A Faraday suit forms an equipotential surface. An E field is the gradient of the voltage. So the Faraday suit forces the E field inside to zero, but does not force the voltage to zero. It is equipotential, not zero potential.